Method and apparatus for closed-loop control of anti-tachyarrhythmia pacing using hemodynamic sensor

ABSTRACT

A cardiac rhythm management (CRM) system includes an implantable medical device that delivers anti-tachyarrhythmia therapies including anti-tachyarrhythmia pacing (ATP) and a hemodynamic sensor that senses a hemodynamic signal. The implantable medical device includes a hemodynamic sensor-controlled closed-loop ATP system that uses the hemodynamic signal for ATP capture verification. When ATP pulses are delivered according to a selected ATP protocol to terminate a tachyarrhythmia episode, the implantable medical device performs the ATP capture verification by detecting an effective cardiac contraction from the hemodynamic signal. The ATP protocol is adjusted using an outcome of the ATP capture verification.

CLAIM OF PRIORITY

This application is a divisional of and claims the benefit of priorityunder 35 U.S.C. §120 to U.S. patent application Ser. No. 11/422,101,filed on Jun. 5, 2006, which is hereby incorporated by reference hereinin its entirety.

TECHNICAL FIELD

This document relates generally to cardiac rhythm management (CRM)systems and particularly to a hemodynamic sensor-controlled closed-loopanti-tachyarrhythmia pacing (ATP) system.

BACKGROUND

Tachyarrhythmias are abnormal heart rhythms characterized by a rapidheart rate. Tachyarrhythmias generally include supraventriculartachyarrhythmia (SVT, including atrial tachyarrhythmia, AT) andventricular tachyarrhythmia (VT). Fibrillation is a form oftachyarrhythmia further characterized by an irregular heart rhythm. In anormal heart, the sinoatrial node, the heart's predominant naturalpacemaker, generates electrical impulses, called action potentials, thatpropagate through an electrical conduction system to the atria and thento the ventricles of the heart to excite the myocardial tissues. Theatria and ventricles contract in the normal atrio-ventricular sequenceand synchrony to result in efficient blood-pumping functions indicatedby a normal hemodynamic performance. VT occurs when the electricalimpulses propagate along a pathologically formed self-sustainingconductive loop within the ventricles or when a natural pacemaker in aventricle usurps control of the heart rate from the sinoatrial node.When the atria and the ventricles become dissociated during VT, theventricles may contract before they are properly filed with blood,resulting in diminished blood flow throughout the body. This conditionbecomes life-threatening when the brain is deprived of sufficient oxygensupply.

Ventricular fibrillation (VF), in particular, stops blood flow withinseconds and, if not timely and effectively treated, causes immediatedeath. In very few instances a heart recovers from VF without treatment.

Cardioversion and defibrillation are used to terminate mosttachyarrhythmias, including AT, VT, and VF. An implantablecardioverter/defibrillator (ICD) is a cardiac rhythm management (CRM)device that delivers an electric shock to terminate a detectedtachyarrhythmia episode by depolarizing the entire myocardiumsimultaneously and rendering it refractory.

Another type of electrical therapy for tachyarrhythmia isanti-tachyarrhythmia pacing (ATP). In ATP, the heart is competitivelypaced in an effort to interrupt the reentrant loop causing thetachyarrhythmia. An exemplary ICD includes ATP and defibrillationcapabilities so that ATP is delivered to the heart when anon-fibrillation VT is detected, while a defibrillation shock isdelivered when fibrillation occurs. Although cardioversion and/ordefibrillation are effective in terminating tachyarrhythmia, it consumesa large amount of power and results in patient discomfort owing to thehigh voltage of the shock pulses. It is desirable, therefore, for theICD to use ATP to terminate a tachyarrhythmia whenever possible.

The efficacy of ATP in terminating tachyarrhythmia depends on the typeof the tachyarrhythmia and the timing of ATP delivery. To be effective,an ATP therapy is to be delivered to the heart during an excitable gapin the reentrant loop. Inaccurate timing of an ATP delivery is known tocontribute to the failure in terminating tachyarrhythmia using ATP.Therefore, in addition to determining whether ATP is suitable fortreating a detected tachyarrhythmia, there is a need to control andoptimize the timing of ATP delivery.

SUMMARY

A CRM system includes an implantable medical device that deliversanti-tachyarrhythmia therapies including ATP and a hemodynamic sensorthat senses a hemodynamic signal. The implantable medical deviceincludes a hemodynamic sensor-controlled closed-loop ATP system thatuses the hemodynamic signal for ATP capture verification. When ATPpulses are delivered according to a selected ATP protocol to terminate atachyarrhythmia episode, the implantable medical device performs the ATPcapture verification by detecting an effective cardiac contraction fromthe hemodynamic signal. The ATP protocol is adjusted using an outcome ofthe ATP capture verification.

In one embodiment, a CRM system includes an implantable hemodynamicsensor and an implantable medical device. The implantable hemodynamicsensor senses a hemodynamic signal. The implantable medical deviceincludes a pacing circuit that delivers pacing pulses, including ATPpulses, and an ATP controller. The ATP controller includes an ATPdelivery controller and an ATP capture verification module. The ATPdelivery controller controls the delivery of the ATP pulses according toan ATP protocol. The ATP capture verification module performs an ATPcapture verification during the delivery of the ATP pulses by detectingan effective cardiac contraction using the hemodynamic signal. Theeffective cardiac contraction is indicated by a detectable event in thehemodynamic signal.

In one embodiment, a method for ATP is provided. A hemodynamic signal issensed. A predetermined type tachyarrhythmia episode is detected. Inresponse to the detection of the predetermined type tachyarrhythmiaepisode, ATP pulses are delivered according to an ATP protocol. An ATPcapture verification is performed during the delivery of the ATP pulsesby detecting an effective cardiac contraction using the hemodynamicsignal. The effective cardiac contraction is indicated by a detectableevent in the hemodynamic signal.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects of the invention will be apparent to persons skilled in the artupon reading and understanding the following detailed description andviewing the drawings that form a part thereof, each of which are not tobe taken in a limiting sense. The scope of the present invention isdefined by the appended claims and their legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings, which are not necessarily drawn to scale, illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 is an illustration of an embodiment of a CRM system including ahemodynamic sensor-controlled closed-loop ATP system and portions of theenvironment in which the CRM system operates.

FIG. 2 is an illustration of an embodiment of the CRM system includingan implantable pulmonary artery pressure (PAP) sensor.

FIG. 3 is a timing diagram illustrating an ATP protocol including ATPparameters.

FIG. 4 is a block diagram illustrating an embodiment of portions of thehemodynamic sensor-controlled closed-loop ATP system.

FIG. 5 is a block diagram illustrating a specific embodiment of portionsof the hemodynamic sensor-controlled closed-loop ATP system.

FIG. 6 is a block diagram illustrating an embodiment of an ATPcontroller of the hemodynamic sensor-controlled closed-loop ATP system.

FIG. 7 is a block diagram illustrating an embodiment of an ATPverification module of the ATP controller.

FIG. 8 is a flow chart illustrating an embodiment of a method forcontrolling ATP using a hemodynamic signal.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the scope of the presentinvention. The following detailed description provides examples, and thescope of the present invention is defined by the appended claims andtheir legal equivalents.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one. In this document, the term“or” is used to refer to a nonexclusive or, unless otherwise indicated.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this documents and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

It should be noted that references to “an”, “one”, or “various”embodiments in this document are not necessarily to the same embodiment,and such references contemplate more than one embodiment.

The relationship between a heart rate and a cardiac cycle length (alsoknown as cardiac interval), as used in this document, is therelationship between a frequency and its corresponding period. If aheart rate is given in beats per minute (bpm), its corresponding cardiaccycle length in milliseconds is calculated by dividing 60,000 by theheart rate (where 60,000 is the number of milliseconds in a minute). Anyprocess, such as a comparison, using a heart rate is to be modifiedaccordingly when a cardiac cycle length is used instead. For example, ifa tachyarrhythmia is detected when the ventricular rate exceeds atachyarrhythmia threshold rate, an equivalent process is to detect thetachyarrhythmia when the ventricular cycle length (also known asventricular interval) falls below a tachyarrhythmia threshold interval.The appended claims should be construed to cover such variations.

This document discusses a CRM system that delivers anti-tachyarrhythmiatherapies including ATP. The ATP delivery is controlled by a closed-loopsystem that automatically verifies whether ATP pulses capture themyocardium and adjusts the ATP delivery based on the outcome of thecapture verification. An ATP therapy for VT includes delivery of one ormore burst of ATP pulses. In an open-loop system, the response to thedelivery of each ATP pulse is not known until a redetection is performedto determine whether the VT sustains after the delivery of a burst ofATP pulses is completed. If the first ATP pulse does not capture themyocardium, one or more remaining ATP pulses of the burst may bedelivered during the heart's vulnerable period, thereby posing a risk ofaccelerating VT to VF. In the present closed-loop system, during adelivery of ATP, the CRM system monitors a hemodynamic signal anddetermines whether each ATP pulse captures the myocardium by analyzingthe effect of the ATP pulse on the hemodynamic signal. When the ATPpulse captures the myocardium, an effective cardiac contraction isindicated by a detectable event in the hemodynamic signal. The effectivecardiac contraction is a cardiac contraction that produces a strokevolume that is considered normal or sufficient. It is detected bycomparing a hemodynamic parameter derived from the hemodynamic signal toa threshold. The detectable event indicative of the effective cardiaccontraction occurs, for example, when the hemodynamic parameter exceedsthe threshold. In one embodiment, the hemodynamic signal is a pressuresignal indicative of cardiac contractions, and a capture verification isperformed by determining whether the ATP pulse results in an effectivecardiac contraction. The effective cardiac contraction is detected whena pressure parameter exceeds a threshold. In other words, a cardiaccontraction is considered effective when it drives a pressure above acertain level. When an ATP pulse captures the myocardium, the CRM systemaborts further delivery of ATP pulses and/or uses the analysis of thehemodynamic signal to optimize ATP parameters for future use. When anATP pulse fails to capture the myocardium, the CRM system adjusts thecurrent ATP protocol including various ATP parameters. This closed-loopcontrol of ATP delivery provides for optimization of ATP therapy foreach individual patient. Because the efficacy of each ATP therapy isknown sooner, this closed-loop control of ATP delivery may allowincreased number of attempts of terminating VT using ATP therapy withoutincreasing the time allocated for ATP before a defibrillation shock.Because the adjustment of the current ATP protocol potentially enhancesthe efficacy of ATP, this closed-loop control of ATP delivery may alsoreduce unnecessary defibrillation shock deliveries.

FIG. 1 is an illustration of an embodiment of a CRM system 100 andportions of the environment in which CRM system 100 operates. CRM system100 includes an implantable medical device 101 that is electricallycoupled to a heart 199 through leads 105 and 110. An external system 102communicates with implantable medical device 101 via a telemetry link103.

Implantable medical device 101 delivers anti-tachyarrhythmia therapiesincluding ATP and cardioversion/defibrillation therapies. In oneembodiment, implantable medical device 101 is an implantablecardioverter/defibrillator (ICD) with cardiac pacing capabilities. Inanother embodiment, in addition to a pacemaker and acardioverter/defibrillator, implantable medical device 101 furtherincludes one or more of other monitoring and/or therapeutic devices suchas a neural stimulator, a drug delivery device, and a biological therapydevice. Implantable medical device 101 includes a hermetically sealedcan housing an electronic circuit that senses physiological signals anddelivers therapeutic electrical pulses. The hermetically sealed can alsofunctions as an electrode for sensing and/or pulse delivery purposes. Inone embodiment, as illustrated in FIG. 1, the electronic circuit sensesat least an atrial electrogram and a ventricular electrogram from heart199 and delivers pacing and cardioversion/defibrillation pulses to heart199. Lead 105 as shown in FIG. 1 is typically a pacing lead thatincludes a proximal end 106 connected to implantable medical device 101and a distal end 107 placed in the right atrium (RA) of heart 199. Apacing-sensing electrode 108 is located at distal end 107. Anotherpacing-sensing electrode 109 is located near distal end 107. Electrodes108 and 109 are electronically connected to implantable medical device101 via separate conductors in lead 105 to allow for sensing of theatrial electrogram and/or delivery of atrial pacing pulses. Lead 110 asshown in FIG. 1 is typically a defibrillation lead that includes aproximal end 111 connected to implantable medical device 101 and adistal end 112 placed in the right ventricle (RV) of heart 199. Apacing-sensing electrode 113 is located at distal end 112. Adefibrillation electrode 114 is located near distal end 112 butelectrically separated from pacing-sensing electrode 113. Anotherdefibrillation electrode 115 is located at a distance from distal end112 for supraventricular placement. Electrodes 113, 114, and 115 areelectrically connected to implantable medical device 101 via separateconductors in lead 110. Electrode 113 allows for sensing of theventricular electrogram and/or delivery of ventricular pacing pulses.Electrodes 114 and 115 allow for sensing of the ventricular electrogramand delivery of ventricular cardioversion/defibrillation pulses.

Implantable medical device 101 includes a hemodynamic sensor-controlledclosed-loop ATP system 120. One or more implantable hemodynamic sensorsare included in, electrically connected to, and/or wirelessly coupled toimplantable medical device 101. System 120 uses at least one hemodynamicsignal sensed by an implantable hemodynamic sensor to perform an ATPcapture verification. An ATP pulse is considered to have captured themyocardium of heart 199 if an effective cardiac contraction is detectedfrom the hemodynamic signal. The capture verification allows foradjustment and optimization of ATP parameters for individual patientsand individual tachyarrhythmia episodes. Various embodiments of system120 are discussed below. In one embodiment, an implantable pressuresensor senses a blood pressure signal used for the ATP captureverification. The blood pressure signal includes features indicative ofcardiac contractions that are detectable by system 120.

External system 102 allows for programming of implantable medical device101 and receives signals acquired by implantable medical device 101. Inone embodiment, external system 102 includes a programmer. In anotherembodiment, external system 102 is a patient management system includingan external device in proximity of implantable medical device 101, aremote device in a relatively distant location, and a telecommunicationnetwork linking the external device and the remote device. The patientmanagement system provides for access to implantable medical device 101from a remote location, such as for monitoring patient status andadjusting therapies. Telemetry link 103 is a wireless communication linkproviding for bidirectional data transmission between implantablemedical device 101 and external system 102. In one embodiment, telemetrylink 103 is an inductive telemetry link. In an alternative embodiment,telemetry link 103 is a far-field radio-frequency telemetry link.Telemetry link 103 provides for data transmission from implantablemedical device 101 to external system 102. This may include, forexample, transmitting real-time physiological data acquired byimplantable medical device 101, extracting physiological data acquiredby and stored in implantable medical device 101, extracting therapyhistory data stored in implantable medical device 101, and extractingdata indicating an operational status of implantable medical device 101(e.g., battery status and lead impedance). Telemetry link 103 alsoprovides for data transmission from external system 102 to implantablemedical device 101. This may include, for example, programmingimplantable medical device 101 to acquire physiological data,programming implantable medical device 101 to perform at least oneself-diagnostic test (such as for a device operational status),programming implantable medical device 101 to enable an availablemonitoring or therapeutic function (such as ATP), and programmingimplantable medical device 101 to adjust therapeutic parameters such aspacing and/or cardioversion/defibrillation parameters.

In various embodiments, system 120, including its various specificembodiments discussed below, is implemented by a combination of hardwareand software. In various embodiments, system 120 includes elements suchas those referred to as modules below that are each anapplication-specific circuit constructed to perform one or moreparticular functions or a general-purpose circuit programmed to performsuch function(s). Such a general-purpose circuit includes, but is notlimited to, a microprocessor or a portion thereof, a microcontroller orportions thereof, and a programmable logic circuit or a portion thereof.

FIG. 2 is an illustration of an embodiment of a CRM system 200 andportions of an environment in which CRM system 200 operates. CRM system200 is a specific embodiment of CRM system 100 and includes animplantable pulmonary artery pressure (PAP) sensor 222, an implantablemedical device 201, leads 105 and 110, external system 102, acommunication link 224 between PAP sensor 222 and implantable medicaldevice 201, and telemetry link 103 between implantable medical device201 and external system 102.

Implantable medical device 201 is a specific embodiment of implantablemedical device 101 and includes a hemodynamic sensor-controlledclosed-loop system 220. System 220 is a specific embodiment of system120 and uses a PAP signal sensed by implantable PAP sensor 222 as thehemodynamic signal to perform the ATP capture verification. The PAPsignal is a specific example of the hemodynamic signal used for the ATPcapture verification discussed in this document. In general, thehemodynamic signal used for the ATP capture verification includes anyblood pressure or other hemodynamic signal from which effective cardiaccontractions can be detected by an implantable medical device.

As illustrated in FIG. 2, implantable PAP sensor 222 and implantablemedical device 201 are implanted in a body 290 that has a pulmonaryartery 298 connected to heart 199. The right ventricle of heart 199pumps blood through pulmonary artery 298 to the lungs of body 290 to getoxygenated. Implantable PAP sensor 222 is a pressure sensor configuredfor being affixed to a portion of the interior wall of pulmonary artery298 to sense a PAP signal. The sensed PAP signal is transmitted toimplantable medical device 201 through communication link 224. In oneembodiment, communication link 224 includes a wired communication linkformed by a lead connected between implantable PAP sensor 222 andimplantable medical device 201. In another embodiment, communicationlink 224 includes an intra-body wireless telemetry link. In a specificembodiment, the intra-body wireless telemetry link is an ultrasonictelemetry link. Implantable medical device 201 includes a sensor signalprocessing system that receives and processes the PAP signal sensed byimplantable PAP sensor 222. In one embodiment, the sensor signalprocessing system processes the PAP signal by removing unwantedcomponents of the signal that potentially affect the accuracy of the ATPcapture verification. In one embodiment, communication link 103 providesfor transmission of data representative of the PAP signal sensed byimplantable PAP sensor 222 and processed and/or stored in implantablemedical device 201. Examples of an implantable PAP sensor and sensorsignal processing are discussed in U.S. patent application Ser. No.11/249,624, entitled “METHOD AND APPARATUS FOR PULMONARY ARTERY PRESSURESIGNAL ISOLATION,” filed on Oct. 13, 2005, now issued as U.S. Pat. No.7,566,308, assigned to Cardiac Pacemakers, Inc., which is incorporatedherein by reference in its entirety.

FIG. 3 is a timing diagram illustrating an ATP protocol including ATPparameters. The illustrated ATP protocol represents a typical protocolin an open-loop ATP system in which no ATP capture verification isperformed to adjust the ATP delivery.

In FIG. 3, each S represents a detected intrinsic ventriculardepolarization, and SL represents the last intrinsic ventriculardepolarization detected before the delivery of a pulse of the ATP pulseis delivered. In response to the detection of a VT episode, an ATPtherapy is delivered. The illustrated ATP protocol provides M bursts ofATP pulses (BURST 1, BURST 2, . . . , BURST M). Each burst includes NATP pulses (P1, P2, P3, PN). BURST 1 is delivered after the VT episodeis detected. In various embodiments, the VT detection includes aninitial detection based on a fast ventricular rate, a verification toconfirm that the fast ventricular rate sustains for a certain duration,and a classification to confirm that the fast ventricular rate has aventricular origin. P1 is delivered when a “coupling interval” expires.The coupling interval (CI) is the time interval between the lastdetected intrinsic ventricular depolarization (SL) and the first ATPpulse of a burst of ATP pulses (i.e., P1). P2 is delivered when a “burstcycle length” expires. The burst cycle length (BCL) is the pacinginterval within the burst of ATP pulses, i.e., the time interval betweentwo successively delivered ATP pulses of the burst of ATP pulses. Inother words, CI is the time between P1 and SL, and BCL is the timeinterval between P(n−1) and P(n), where 2≦n≦N.

The VT episode is redetected following each burst of ATP pulses isdelivered. If the VT episode sustains, the ATP therapy may continue bydelivering another burst of ATP pulses. The delivery of the burst of ATPpulses and the VT redetection are repeated until the episode is notredetected or until BURST M has been delivered. If the VT episode issustains after BURST M has been delivered, one or more defibrillationshocks are delivered to terminate the VT episode.

During the ATP therapy, the BCL may be a constant or varying timeinterval. A “burst” scheme of BCL refers to a BCL that is a constanttime interval throughout the ATP therapy. A “ramp” scheme of BCL refersto a BCL that is decremental within each burst of ATP pulses. A “scan”scheme of BCL refers to a BCL that is decremental from a burst of ATPpulses to the next burst of ATP pulses within an ATP therapy. In variousembodiment, an ATP protocol includes a plurality of ATP parametersincluding CI, BCL, BCL scheme (burst, ramp, or scan), number of pulsesper burst (N), and number of burst per ATP therapy (per ATPprotocol)(M).

In a typical open-loop ATP system, the effect of the ATP pulses is notknown until the VT redetection period that follows. Consequently, someof the ATP pulses may be unnecessary, ineffective, or even risky. Asdiscussed in detail below, a hemodynamic signal-based ATP captureverification during the delivery of each burst of ATP pulses eliminatesthe delivery of such unnecessary, ineffective, or risky ATP pulses.

FIG. 4 is a block diagram illustrating an embodiment of portions ofsystem 100, including an implantable hemodynamic sensor 422, animplantable medical device 401, and communication link 224. Implantablehemodynamic sensor 422 senses a hemodynamic signal indicative of cardiaccontractions. Implantable medical device 401 is a specific embodiment ofimplantable medical device 101 and includes a sensing circuit 430, apacing circuit 432, and an ATP controller 434. Sensing circuit 430senses one or more cardiac signals. Pacing circuit 432 delivers pacingpulses including ATP pulses. ATP controller 434 includes an ATP deliverycontroller 436 and an ATP capture verification module 438. ATP deliverycontroller 436 controls the delivery of the ATP pulses according to anATP protocol. ATP capture verification module 438 performs an ATPcapture verification during the delivery of the ATP pulses by detectingan effective cardiac contraction using the hemodynamic signal sensed byimplantable hemodynamic sensor 422.

FIG. 5 is a block diagram illustrating a specific embodiment of portionsof system 100, including an implantable pressure sensor 522, animplantable medical device 501, and communication link 224.

Implantable pressure sensor 522 is a specific embodiment of implantablehemodynamic sensor 422 and senses a blood pressure signal indicative ofcardiac contractions. In one embodiment, implantable pressure sensor 522is an implantable PAP sensor configured to be placed in the pulmonaryartery and communicatively coupled to implantable medical device 501 viacommunication link 224, such as implantable PAP sensor 222. In oneembodiment, implantable pressure sensor 522 includes a pressure sensingdevice 540 and a sensor telemetry circuit 542. Pressure sensing device540 is a transducer that converts a pressure to an electrical signal.Sensor telemetry circuit 542 transmits data representative of the PAPsignal to implantable medical device 501 via communication link 224,which is a telemetry link such as an ultrasonic telemetry link. In otherembodiments, implantable pressure sensor 522 is included in implantablemedical device 501 or electrically connected to implantable medicaldevice 501 via a lead.

Implantable medical device 501 is a specific embodiment of implantablemedical device 401 and includes implant telemetry circuit 544, sensorprocessing circuit 546, sensing circuit 430, pacing circuit 432,defibrillation circuit 548, and implant controller 550. Implanttelemetry circuit 544 receives the blood pressure signal sensed byimplantable pressure sensor 522 and transmitted via communication link224. In addition, implant telemetry circuit 544 transmits data to, andreceives data from, external system 102 via telemetry link 103. In oneembodiment, communication link 224 is an acoustic telemetry link, andtelemetry link 103 is an RF telemetry link. Implant telemetry circuit544 includes an implant acoustic telemetry circuit to transmit andreceive signals via the acoustic telemetry link and an implant RFtelemetry circuit to transmit and receive signals via the RF telemetrylink. Sensor processing circuit 546 processes the blood pressure signalto allow or facilitate the detection of effective cardiac contractions.In one embodiment, sensor processing circuit 546 includes a sensorcalibration module 547 that removes environmental effects from the bloodpressure signal. In various embodiments, sensor processing circuit 546removes components of the blood pressure signal that affect accuracy ofthe detection of effective cardiac contractions. For example, effects ofrespiration on the blood pressure signal is removed by filtering, andeffects of posture on the blood pressure signal is removed by using aposture signal sensed by a posture sensor. In one embodiment, the bloodpressure signal is a PAP signal. Examples of processing a PAP signal isdiscussed in U.S. patent application Ser. No. 11/249,624.

Sensing circuit 430 senses one or more cardiac signals. Pacing circuit432 deliver pacing pulses including ATP pulses. Defibrillation circuit548 delivers cardioversion/defibrillation shocks. Implant controller 550includes a pacing controller 552, defibrillation controller 554,tachyarrhythmia detector 556, and ATP controller 534. Pacing controller552 controls the delivery of the pacing pulses. In one embodiment, asillustrated in FIG. 5, ATP controller 534 controls the delivery of theATP pulses through pacing controller 552. For example, ATP controller534 executes the ATP protocol to generate ATP pulse delivery signals,and pacing controller 552 directly controls the delivery of the pacingpulses from pacing circuit 432 using the delivery timing signals.Defibrillation controller 554 controls the delivery ofcardioversion/defibrillation shocks. Tachyarrhythmia detector 556detects tachyarrhythmia episodes and identifies predetermined typetachyarrhythmia episodes that are likely terminable by ATP. In oneembodiment, the predetermined type tachyarrhythmia episodes include VTepisodes, and tachyarrhythmia detector 556 includes a VT detector todetect VT episodes. The VT detector performs the VT detection andredetections illustrated in FIG. 3. In one embodiment, the VT detectordetects and confirms VT before ATP controller 534 is activated tocontrol the delivery of an ATP therapy. In one embodiment, the VTdetector also extracts parameters indicative of characteristics of theVT episode from at least the one or more cardiac signals, such as heartrate and heart rate stability parameters.

ATP controller 534 is a specific embodiment of ATP controller 434 andincludes an ATP delivery controller 536 and an ATP capture verificationmodule 538. ATP delivery controller 536 controls the delivery of the ATPpulses according to the ATP protocol. ATP capture verification module538 performs an ATP capture verification during the delivery of the ATPpulses by detecting an effective cardiac contraction using the bloodpressure signal.

FIG. 6 is a block diagram illustrating an embodiment of an ATPcontroller 634, which is a specific embodiment of ATP controller 434 or534. ATP controller 634 controls an ATP therapy in response to thedetection of the predetermined type tachyarrhythmia episode such as theVT episode. ATP controller 634 includes an ATP delivery controller 636,an ATP capture verification module 638, an ATP protocol selector 658, anATP adjustment module 662, a memory circuit 660, an ATP library updatemodule 664, and a protocol prioritization module 668.

ATP delivery controller 636 is a specific embodiment of ATP deliverycontroller 436 or 536 and controls the delivery of the ATP pulsesaccording to a selected ATP protocol. In one embodiment, ATP deliverycontroller 636 is activated when a VT episode is detected and confirmed.ATP delivery controller 636 is reset to switch from the selected ATPprotocol to a new ATP protocol in response to a reset signal produced asan outcome of the ATP capture verification. That is, in response to thereset signal, ATP delivery controller 636 stops controlling the deliveryof the ATP pulses according to the selected ATP protocol and starts tocontrol the delivery of the ATP pulses according to a new ATP protocol.ATP capture verification module 638 is a specific embodiment of ATPcapture verification module 438 or 538 and performs the ATP captureverification by extracting a hemodynamic parameter from the hemodynamicsignal and comparing the hemodynamic parameter to a capture threshold todetect effective cardiac contractions. ATP capture verification module638 is further discussed below with reference to FIG. 7.

ATP protocol selector 658 selects the ATP protocol from a plurality ofstored ATP protocols. In one embodiment, ATP protocol selector 658selects the ATP protocol based on the parameters indicative ofcharacteristics of the tachyarrhythmia episode, such as heart rate andheart rate stability parameters produced by tachyarrhythmia detector556. In another embodiment, ATP protocol selector 658 selects the ATPprotocol based on a priority code assigned to each of the stored ATPprotocols.

ATP adjustment module 662 adjusts the ATP protocol based on an outcomeof the ATP capture verification. If an ATP capture is verified (aneffective cardiac contraction is detected by ATP capture verificationmodule 638), in one embodiment, the delivery of the ATP pulses accordingto the selected ATP protocol is aborted, and the tachyarrhythmia episodeis redetected to determine whether it has been terminated. In anotherembodiment, the delivery of the ATP pulses according to the selected ATPprotocol is completed to evaluate the selected ATP protocol for ATPparameter optimization purposes. In one embodiment, ATP adjustmentmodule 662 produces a new ATP protocol by using values of the ATPparameters associated with the a verified ATP capture. If no ATP captureis verified (i.e., a loss of capture is verified), in one embodiment,ATP adjustment module 662 aborts the delivery of the ATP pulses,produces a new ATP protocol, and produces the reset signal to reset ATPdelivery controller 636. In one embodiment, ATP adjustment module 662produces the new ATP protocol by adjusting the ATP parameters of theselected protocol, such as by increasing CI, increasing BCL, and/orchanging BCL scheme. In another embodiment, ATP adjustment module 662produces the new ATP protocol by selecting another ATP protocol from theplurality of store ATP protocols. In one embodiment, ATP adjustmentmodule 662 repeats producing the reset signal and the new ATP protocolif no ATP capture is verified for up to a predetermined number of times(such as 4 times). If the delivery of the ATP pulses is aborted becausethe ATP capture is not verified, there is no need to determine whetherhemodynamic episode has been terminated by ATP.

Memory circuit 660 is a data storage device that includes an ATP library661. ATP library 661 includes the plurality of stored ATP protocols. ATPlibrary update module 664 updates ATP library 661 after each delivery ofthe ATP therapy. In one embodiment, ATP library update module 664updates a success rate associated with each of the stored ATP protocols.The success rate is statistically produced and updated to indicate alikeliness of terminating a tachyarrhythmia episode using the associatedATP protocol. In one embodiment, the parameters indicative ofcharacteristics of a particular tachyarrhythmia episode, such as heartrate and heart rate stability parameters, are also stored in associationwith a stored ATP protocol that has been used to successfully terminatethat particular tachyarrhythmia episode. In one embodiment, if an ATPprotocol is adjusted by ATP adjustment module 662 during an ATP therapy,and the adjusted protocol is used to successfully terminate atachyarrhythmia episode, the adjusted (new) ATP protocol is added to theplurality of stored ATP protocols in ATP library 661.

Protocol prioritization module 668 assigns the priority code to each ofthe stored ATP protocols based on the success rate associated with thatstored ATP protocol. In one embodiment, protocol prioritization module668 also assigns the priority code based on the parameters of the storedATP protocol. For example, a higher priority is given to an ATP protocolthat has relatively fewer ATP pulses per burst or otherwise requiresless time to deliver the ATP pulses.

FIG. 7 is a block diagram illustrating an embodiment of an ATP captureverification module 738. ATP verification module 738 is a specialembodiment of ATP verification module 638 and includes a signal input770, a signal analyzer 772, a contraction detector 774, and a thresholdgenerator 776.

Signal input 770 receives the hemodynamic signal. Signal analyzer 772extracts the hemodynamic parameter from the hemodynamic signal.Contraction detector 774 detects the effective cardiac contraction bycomparing the hemodynamic parameter to the capture threshold. Thresholdgenerator 776 produces the capture threshold. In one embodiment,threshold generator 776 produces the capture threshold based on abaseline value of the hemodynamic parameter extracted from thehemodynamic signal sensed during a normal sinus rhythm. The capturethreshold is set to a predetermined percentage of the baseline value ofthe hemodynamic parameter.

In one embodiment, in which the hemodynamic signal is a blood pressuresignal such as a PAP signal, ATP capture verification module 738performs the ATP capture verification by detecting effective cardiaccontractions from the blood pressure signal during the ATP therapy.Signal input 770 receives the blood pressure signal. Signal analyzer 772extracts a pressure parameter from the pressure signal. In oneembodiment, the pressure parameter is a pulse pressure being adifference between a systolic pressure and a diastolic pressure. Usingthe pulse pressure for ATP capture verification has an advantage ofbeing able to ignore many unwanted components because they are canceledout when the difference is calculated. When desired, this allowssuspension of the hemodynamic signal calibration during the ATP therapy.In another embodiment, the pressure parameter is mean pressure being theamplitude of the blood pressure signal averaged over a predeterminedtime interval or a predetermined number of heart beats. The meanpressure represents the DC or low-frequency component of the bloodpressure signal. In another embodiment, the pressure parameter is a peakpressure being a peak amplitude of the blood pressure signal. In anotherembodiment, the pressure parameter is a pressure power being a power ina predetermined frequency band. Contraction detector 774 detects evokedpressure responses each indicative of an effective cardiac contractionby comparing the pressure parameter to a capture threshold pressure.Threshold generator 776 produces the capture threshold pressure. In oneembodiment, threshold generator 776 produces the capture thresholdpressure based on a baseline value of the pressure parameter extractedfrom the blood pressure signal sensed during a normal sinus rhythm. Thecapture threshold pressure is set to a predetermined percentage of thebaseline value of the pressure parameter.

FIG. 8 is a flow chart illustrating an embodiment of a method 800 forcontrolling ATP using a hemodynamic signal. In one embodiment, method800 is performed by system 100, including its various embodimentsdiscussed in this document.

One or more cardiac signals are sensed at 802. A hemodynamic signal issensed at 804. In one embodiment, the hemodynamic signal is a bloodpressure signal. In one embodiment, the hemodynamic signal is processedto remove unwanted components such as effects of respiration and effectsof posture. In a specific embodiment, the blood pressure signal is a PAPsignal sensed using an implantable PAP sensor configured to be placed inthe pulmonary artery. Examples of sensing and processing a PAP signalare discussed in U.S. patent application Ser. No. 11/249,624, now issuedas U.S. Pat. No. 7,566,308.

A predetermined type tachyarrhythmia episode is being detected at 806.This predetermined type is known to be likely terminable by ATP, such asmonomorphic VT. In one embodiment, a VT episode is detected when a fastventricular rate is detected, verified to be sustaining, and confirmedto be of a ventricular origin. In one embodiment, parameters indicativeof characteristics of the detected tachyarrhythmia episode, such as theheart rate and heart rate stability, are extracted from at least the oneor more cardiac signals for storage in association with a stored ATPprotocol that has been used to successfully terminate thattachyarrhythmia episode.

If the predetermined type tachyarrhythmia episode is not detected at808, a baseline value of a hemodynamic parameter may be measured at 810.In one embodiment, the hemodynamic signal is a blood pressure signal,and the hemodynamic parameter is a pressure parameter. A capturethreshold is produced at 812 using the measured baseline value. In oneembodiment, the capture threshold is set to a predetermined percentageof the baseline value. In one embodiment, the capture threshold isupdated substantially continuously to follow the change in the baselinepressure in a patient. In another embodiment, the capture threshold isupdated on a periodic basis. In another embodiment, the capturethreshold is updated upon a user request.

If the predetermined type tachyarrhythmia episode is detected at 808, anATP protocol is selected from a plurality of stored ATP protocols at814. In one embodiment, the ATP protocol is selected based on theparameters indicative of characteristics of the detected tachyarrhythmiaepisode. In one embodiment, the ATP protocol is selected based on apriority code assigned to each of the stored ATP protocols. The prioritycode is produced based on the historical performance of each stored ATPprotocol and the parameters of that ATP protocol.

A burst of ATP pulses is to be delivered with the number of ATP pulsesspecified in the selected ATP protocol. If an ATP pulse count is greaterthan zero (i.e., there are remaining ATP pulse(s) to be delivered) at816, an ATP pulse is delivered at 818. A capture verification isperformed at 820. The ATP capture verification includes determiningwhether the ATP pulse delivered at 818 causes an effective cardiaccontraction. The hemodynamic parameter is extracted from the hemodynamicsignal sensed during the ATP therapy. The effective cardiac contractionis detected by comparing the hemodynamic parameter to the capturethreshold. In one embodiment, the hemodynamic signal is a blood pressuresignal. A pressure parameter is extracted from the pressure signalsensed during the ATP therapy. Examples of the pressure parameterincludes a pulse pressure being a difference between a systolic pressureand a diastolic pressure, a mean pressure being an average amplitude (DCor low-frequency value) of the pressure signal, a peak pressure, and apressure power being a power in a predetermined frequency band. Anevoked pressure response indicative of an effective cardiac contractionis detected by comparing the pressure parameter to a capture thresholdpressure.

If the myocardium is captured at 822, and the ATP pulse count is greaterthan zero at 816, another ATP pulse is delivered at 818. If themyocardium is captured at 822, and the ATP pulse count reaches zero at816, the tachyarrhythmia episode is redetected at 828. In oneembodiment, if the myocardium is captured at 822, the ATP pulse count isset to zero, thereby aborting further delivery of the ATP pulses. Inanother embodiment, if the myocardium is captured at 822, the ATP pulsesare continued to be delivered according to the selected ATP protocol forthe purpose of evaluating the parameters of the selected ATP protocolfor protocol optimization.

If the myocardium is not captured at 822, the selected ATP protocol isaborted and adjusted to produce a new ATP protocol at 824. In oneembodiment, the new ATP protocol is produced by adjusting ATPparameters, such as by increasing CI, increasing BCL, and/or changingthe BCL scheme from burst to ramp. In another embodiment, the new ATPprotocol is produced by selecting another ATP protocol from theplurality of store ATP protocols.

The ATP pulse count is reset at 826. The delivery of the ATP pulses isrestarted according to the new ATP protocol. Steps 816, 818, 820, 822,824, and 826 are repeated until the ATP pulse count equals zero at 816.The ATP pulse count reaches zero at 816 when the ATP capture isverified, when a complete burst of ATP pulses is delivered, or when theATP pulse count is otherwise set to zero as programmed.

If the ATP pulse count equals zero at 816, the tachyarrhythmia episodeis redetected at 828 to determine whether the tachyarrhythmia episodesustains. If the tachyarrhythmia episode has been terminated at 830, theATP library is updated at 836. In one embodiment, a success rateassociated with each stored ATP protocol is updated each time when thatstored ATP protocol is used to reflect the efficacy of ATP therapyassociated with that stored ATP protocol. In one embodiment, theparameters indicative of the characteristics of the tachyarrhythmiaepisode associated with that stored ATP protocol are also stored toallow future ATP protocol selection using parameter matching as afactor. In one embodiment, the new ATP protocol produced during the ATPtherapy by adjusting the selected ATP protocol is added to the pluralityof stored ATP protocols if the tachyarrhythmia episode is terminated inresponse to the delivery of the ATP pulses according to the new ATPprotocol. In one embodiment, the priority code of each of the stored ATPprotocols is updated after each ATP therapy to reflect the result ofthat ATP therapy in association with the stored ATP protocols.

If the tachyarrhythmia episode is not terminated at 830, and noadditional ATP attempt is to be made at 832, a defibrillation shock isdelivered at 834. Steps 828, 830, 832, and 834 are repeated until thetachyarrhythmia episode is terminated at 830 or until a certain numberof defibrillation shocks have been delivered. Generally, if adefibrillation shock has been delivered at 834, no additional ATPattempt is to be made at 832.

If the tachyarrhythmia episode is not terminated at 830, and anadditional ATP attempt is to be made at 832, method 800 is repeated fromselecting another ATP protocol at 814. In one embodiment, additional ATPattempts are made until a predetermined maximum number of ATP attemptshave been made. If the tachyarrhythmia is terminated at 830 followingthe delivery of the defibrillation shock at 834, the success rateassociated with each stored ATP protocol used in the ATP attempt(s) isupdated to reflect the unsuccessful attempt(s) associated with thatstored ATP protocol.

It is to be understood that the above detailed description is intendedto be illustrative, and not restrictive. Other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. A method for anti-tachyarrhythmia pacing (ATP), the methodcomprising: sensing a hemodynamic signal; detecting a predetermined typetachyarrhythmia episode; delivering ATP pulses according to an ATPprotocol in response to the detection of the predetermined typetachyarrhythmia episode; and performing an ATP capture verificationduring the delivery of the ATP pulses by detecting an effective cardiaccontraction using the hemodynamic signal, the effective cardiaccontraction indicated by a detectable event in the hemodynamic signal.2. The method of claim 1, wherein performing the ATP captureverification comprises: extracting a hemodynamic parameter from thehemodynamic signal; and detecting the effective cardiac contraction bycomparing the hemodynamic parameter to a capture threshold.
 3. Themethod of claim 2, wherein sensing the hemodynamic signal comprisessensing a blood pressure signal, and performing the ATP captureverification comprises: extracting a pressure parameter from thepressure signal; and detecting an evoked pressure response indicative ofthe effective cardiac contraction by comparing the pressure parameter toa capture threshold pressure.
 4. The method of claim 3, whereinextracting the pressure parameter comprises extracting a pulse pressurebeing a difference between a systolic pressure and a diastolic pressure.5. The method of claim 3, wherein extracting the pressure parametercomprises extracting a mean pressure being an amplitude of the bloodpressure signal averaged over a predetermined duration or a predeterminenumber of heart beats.
 6. The method of claim 3, wherein sensing theblood pressure signal comprises sensing an pulmonary artery pressure(PAP) signal using an implantable PAP sensor.
 7. The method of claim 1,further comprising adjusting the ATP protocol based on an outcome of theATP capture verification.
 8. The method of claim 7, further comprisingaborting the delivery of the ATP pulses if the effective cardiaccontraction is detected.
 9. The method of claim 7, further comprisingaborting the delivery of the ATP pulses and delivering additional ATPpacing pulses according to a new ATP protocol if the effective cardiaccontraction is not detected.
 10. The method of claim 9, furthercomprising producing the new ATP protocol by adjusting ATP parameters ofthe ATP protocol.
 11. The method of claim 9, further comprisingproducing the new ATP protocol by selecting another ATP protocol from aplurality of stored ATP protocols.
 12. The method of claim 11, furthercomprising: maintaining an ATP library including a plurality of storedATP protocols each including a plurality of ATP parameters; andselecting the ATP protocol from the plurality of stored ATP protocolsbased on priority codes each associated with one ATP protocol of theplurality of stored ATP protocols.
 13. The method of claim 12, whereinmaintaining the ATP library comprises: updating a success rateassociated with the ATP protocol based on an outcome of the captureverification; and adjusting the priority codes based on the successrates associated with the stored ATP protocols and the ATP parameters ofthe stored ATP protocols.
 14. The method of claim 12, furthercomprising: sensing one or more cardiac signals; detecting thepredetermined type tachyarrhythmia episode using the one or more cardiacsignals; and extracting parameters indicative of characteristics of thedetected predetermined type tachyarrhythmia episode from at least theone or more cardiac signals, and wherein selecting the ATP protocolcomprises selecting the ATP protocol from the plurality of stored ATPprotocols based on the parameters indicative of characteristics of thedetected predetermined type tachyarrhythmia episode and the prioritycodes.
 15. A method for anti-tachyarrhythmia pacing (ATP), the methodcomprising: receiving a pulmonary artery pressure (PAP) signal;detecting a tachyarrhythmia episode; delivering ATP pulses from animplantable medical device according to an ATP protocol in response tothe detection of the tachyarrhythmia episode; and performing an ATPcapture verification during the delivery of the ATP pulses by detectingan effective cardiac contraction using the PAP signal.
 16. The method ofclaim 15, wherein receiving the PAP signal comprises receiving the PAPsignal from an implantable PAP sensor placed in a pulmonary artery andcommunicatively coupled to the implantable medical device.
 17. Themethod of claim 16, wherein receiving the PAP signal from theimplantable PAP sensor comprises receiving the PAP signal from theimplantable PAP sensor via a wireless telemetry link.
 18. The method ofclaim 17, wherein receiving the PAP signal from the implantable PAPsensor comprises receiving the PAP signal from the implantable PAPsensor via an ultrasonic telemetry link.
 19. The method of claim 15,comprising: sensing one or more cardiac signals; detecting a ventriculartachyarrhythmia (VT) episode; extracting parameters indicative ofcharacteristics of the detected VT episode from at least the one or morecardiac signals; and selecting the ATP protocol from an ATP librarybased on the parameters indicative of the characteristics of thedetected VT episode, the ATP library including a plurality of stored ATPprotocols.
 20. The method of claim 19, wherein selecting the ATPprotocol comprises selecting the ATP protocol based on a priority codeassigned to each of the stored ATP protocols, and further comprisingupdating the ATP library, including updating the priority codes, usingan outcome of the ATP capture verification.